75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

169 Identification of Genes Expressed in the Arabidopsis Female Gametophyte
Joshua Steffen, Il-Ho Kang, Jane Macfarlane, Gary Drews
University of Utah
The Arabidopsis female gametophyte (FG) is composed of 1 egg cell, 1 central cell, 2 synergid cells, and 3 antipodal
cells. The FG plays a role in many stages of the reproductive process including pollen tube guidance, double fertilization,
induction of seed development, and maternal control of embryo and endosperm development. The molecular processes
by which the female gametophyte cells acquire their unique features and functions during cell differentiation are not
understood. As a first step toward dissecting the gene regulatory networks controlling cell specification and differentiation
during FG development, we have used expression assays to identify a collection of genes expressed in the Arabidopsis
FG.
We carried out a differential microarray screen to identify genes expressed in the female gametophyte. Our general
strategy was to identify mRNAs present in WT ovules but not in mutant ovules lacking FGs. Using microarrays we
identified 86 genes that have reduced expression in mutant ovules. To validate the expression patterns of these genes,
we carried out real-time RT-PCR assays with RNA from independently harvested ovules. Using the criteria of ≥8-fold
change, 71 of the 86 genes were validated as having reduced expression in mutant ovules. To determine which cells
within the female gametophyte these genes are expressed within, we generated Promoter:GFP gene fusions. Analysis
of promoter-GFP transgenic plant is in progress. The identification of genes expressed within specific cells of the FG
allows us to take the first steps towards dissecting gene regulatory networks controlling cell differentiation during FG
development.
170 Direct regulation of the floral homeotic APETALA1 gene by APETALA3 and PISTILLATA in
Arabidopsis
Jens Sundstrom 1, 2 , Naomi Nakayama 2 , Kristina Glimelius 1 , Vivian Irish 2
1
Swedish Agricultural University, 2 Yale University
The floral homeotic gene APETALA1 (AP1) specifies floral meristem identity and sepal and petal identity in
Arabidopsis. Consistent with its multiple roles during floral development, AP1 is initially expressed throughout the floral
meristem, and later its expression becomes restricted to sepal and petal primordia. Using Chromatin Immunoprecipitation
we show that the floral homeotic PISTILLATA (PI) protein, required for petal and stamen development, has the ability to
bind directly to the promoter region of AP1. In support of the hypothesis that PI, and its interacting partner APETALA3
(AP3), regulates the transcription of AP1 we show that AP1 transcript levels are elevated in strong ap3-3 mutant plants.
Kinetic studies, using transgenic Arabidopsis plants in which both AP3 and PI are under posttranslational control, show
that AP1 transcript levels are down regulated within 2 hours of AP3/PI activation. This implies that the reduction of AP1
transcripts is an early event in the cascade following AP3/PI induction and provides independent support for the hypothesis
that AP1 is a direct target of the AP3/PI heterodimer. Together, these results suggest a model whereby AP3/PI directly
acts, in combination with other factors, to restrict the expression of AP1 during early stages of floral development.